Electrical power cables are frequently constructed with a composite insulating covering of a plurality of layers or units. For example, power cables of medium-to-high voltage capacity, such as 15 KV and higher, are commonly provided with one or more bodies of shielding semiconductive material adjacent to the body of the primary dielectric insulation as is illustrated in U.S. Pat. Nos. 3,096,210; 3,259,688; 3,287,489; 3,482,033; 3,541,228; 3,569,610, and many other patents.
However, in such high voltage carrying cables, the presence of flaws in the covering body enclosing the conductor, such as air spaces, pores or voids, cause faults which result in failure of the insulation and in turn the cable. The magnitude of this problem of voids or breaks in cable insulating coverings is indicated by many recent U.S. Pat. Nos. 3,527,874; 3,629,110; 3,646,248; 3,666,874; and 3,793,476.
The occurrence of flaws such as voids or breaks in semiconducting polymeric materials or shields overlying the primary body of dielectric insulation of electric cables, due, for example, to problems with the stock material, production processes such as extrusion, or whatever cause, constitutes a significant and costly defect in cable products, often necessitating the cutting out of sections of expensive high voltage cables to remove defective portions therefrom.
Remedial efforts to patch such faults in multilayered cable constructions comprising cured or thermoset polymeric dielectric insulations and/or semiconductive shields with a material of the same or similar composition as that containing the defect have encountered serious problems. The subsequent curing of the applied patching material by the usual heat curing systems and means has generally caused a separation of the layers of material adjacent to the patched area, and/or the development of internal pores in the material adjacent to the patched area constituting new voids or faults which likewise degrade the electrical properties of the cable and its performance life.